In a typical wireless communication network, wireless devices, also known e.g. as user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks. The RAN covers a geographical area which traditionally is divided into cell areas, with each cell area being served by a network node such as a radio access node or base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not co-located. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole wireless communication network is also broadcasted in the cell. One network node may have one or more cells. The network nodes communicate over the air interface operating on radio frequencies with the wireless devices within range of the network nodes with downlink transmissions towards the wireless devices and uplink transmission from the wireless devices.
A Universal Mobile Telecommunications System (UMTS) is a third generation wireless communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for wireless devices. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some versions of the RAN as e.g. in UMTS, several network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS) have been completed within the 3GPP and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the network nodes, such as radio access nodes or base stations, are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNC are distributed between the radio access nodes or base stations, e.g. eNodeBs in LTE, and the core network. As such, the Radio Access Network (RAN) of an EPS has an essentially “flat” architecture comprising radio access nodes that do not report to RNCs.
The 3GPP initiative “License Assisted Access” (LAA) aims to allow LTE equipment to operate in an unlicensed 5 GHz radio spectrum. The unlicensed 5 GHz spectrum is used as an extension to the licensed spectrum. For example, wireless devices may connect in the licensed spectrum to a primary cell (PCell), and use carrier aggregation to benefit from additional transmission capacity in the unlicensed spectrum in a secondary cell (SCell). To reduce the changes required for aggregating licensed and unlicensed spectrum, an LTE frame timing in the primary cell may simultaneously be used in the secondary cell.
Regulatory requirements, however, may not permit transmissions in the unlicensed spectrum without prior channel sensing. Since the unlicensed spectrum must be shared with other radios of similar or dissimilar wireless technologies, a so called Listen-Before-Talk (LBT) method needs to be applied. Today, the unlicensed 5 GHz spectrum is mainly used by communication terminals implementing the IEEE 802.11 Wireless Local Area Network (WLAN) standard. This standard is known under its marketing brand “Wi-Fi.”
IEEE 802.11 equipment, also called WLAN equipment, uses a contention based medium access scheme. This scheme does not allow a wireless medium to be reserved at specific instances of time. Instead, IEEE 802.11 equipment or IEEE 802.11 compliant devices only support the immediate reservation of the wireless medium following the transmission of at least one medium reservation message, e.g. Request to Send (RTS) or Clear to Send (CTS) or others. To allow the Licensed Assisted (LA)-LTE frame in the secondary cell to be transmitted at recurring time intervals that are mandated by the LTE frame in the primary cell, the LAA system transmits at least one of the aforementioned medium reservation messages to block surrounding IEEE 802.11 equipment from accessing the wireless medium.
A wireless device in a communication network may enter a so-called idle mode, in which it does not actively communicate with network nodes. In idle mode, wireless devices may move through the communication network without performing explicit handovers when moving from an area covered by one network node, e.g. a radio access node or a base station, into an area covered by another network node, e.g. another radio access node or base station. When the network node needs to reach a wireless device which is in idle mode, e.g. when someone is making a phone call to the wireless device, a so-called “paging” is performed. To perform the paging, i.e. to page the wireless device, a network node sends a paging message when the wireless device is assumed to be located within the coverage area of the network node. The paging message comprises an identity, which may be used by the wireless device to recognize the paging message as a paging message targeting the wireless device. When no reply is received from the wireless device when paged in the coverage area of a cell served by the network node, the wireless device may be paged in an increased number of cells, which may or may not be served by the same network node, e.g. until the wireless device responds or until the wireless device has been paged in a certain area. According to current 3GPP standards, the network configures in which sub-frames a wireless device should wake up and listen for paging. Such a configuration is performed when the wireless device is in connected mode, and is then applied when the wireless device is in idle mode.
In LTE, so far, a wireless device in idle mode listens for reference signals, such as primary and secondary synchronization signals of a cell, in order to “camp” on the cell while being in the coverage area of the cell. The expression “to camp on a cell” implies that the wireless device has retrieved, by listening to cell-specific reference signals, knowledge of the configuration of the cell, including a physical cell ID of the cell and information enabling initial access to the cell, such as a demodulation sequence, random access configuration and power control settings, etc. When a wireless device in idle mode moves into the coverage area of a new cell, possibly served by a new network node, it listens for reference signals related to the cell in order to camp on the new cell. By camping on a cell, the wireless device is synchronized with the cell and is able to receive and decode paging messages transmitted in the cell. While camping on a specific cell, the wireless device does not listen for reference signals related to other cells or network nodes.
Today, at least in LTE networks, a network node, e.g. a radio access node or a base station, sends cell-specific reference signals in the whole coverage area of a cell associated with the network node at regular intervals. However, in future implementations of wireless communication networks, the coverage area of a “cell” of a network node is expected to be more dynamic, e.g. due to the introduction of advanced beam forming solutions. That is, a predefined coverage area of a network node, i.e. what today is known as a cell, will not be continuously covered anymore. Instead coverage is expected to be provided where needed in a coverable area. Further, contention based access is expected to be implemented, which implies that radio resources cannot be constantly dedicated, in a pre-determined manner, for a certain type of transmissions such as downlink control channels and paging channels. Furthermore, it is expected that a wireless device that is not in connected mode need not necessarily be in idle mode according to the conventional understanding of what is meant by being in idle mode. As an example, a wireless device may be in a “dormant mode”, where the wireless device keeps its context without being available to communicate with the wireless communication network as would be done when being in connected mode.
Further, a future communication network scenario is expected to comprise a very large number of machine-type-communication (MTC) devices. Many such devices are expected to transmit small amounts of uplink (UL) data, e.g. 100 bits, more seldom, e.g. once per hour, or more often, e.g. once every second. In general, such devices often have high requirements on battery life, i.e. on low energy consumption, and also on low cost. These requirements imply that efficient and long discontinuous reception (DTX) and transmission (DTX) cycles, i.e. periods when the devices are in non-active, e.g. idle or dormant, mode, are wanted, and also that the MTC devices should preferably be operated on a small bandwidth, both for energy and cost reasons.
Further, in future communication networks solutions, e.g. what may be referred to as 5G, network nodes can potentially be configured in different ways to meet different service requirements. In fact, in 5G the network will most likely make use of different configurations depending e.g. on the radio services around a network node. In addition to the different configurations of network nodes, wireless devices may also be of different capabilities and also be configured for different behavior. This may lead to problems in certain situations, such as when a wireless device should “wake up” from a non-active mode, such as idle mode or a dormant mode, and listen for paging messages. For example, when a wireless device wakes up to monitor for signaling from the network, e.g. for paging, the configuration of the network node that the wireless device can receive paging from may have changed compared to when the wireless device was configured by the network for paging. The network node may or may not be same as when the wireless device went into non-active mode, meaning that the configuration of the network node may have changed due to re-configuration of the network node and/or due to mobility of the wireless device.
Consequently, in future communication systems as described above, wireless devices in idle mode would no longer be reached by a paging mechanism relying on that paging messages are scheduled for transmission over the radio interface according to a in the wireless device a priori known timing, as done according to e.g. currently used 3GPP standards for communication.